Initial mobile support (Android and iOS)

[felselva]

I'm still not sure how the support for mobile will be done, but it might be similar to the support for Emscripten (https://github.com/ferreiradaselva/swfw/issues/1) regarding the context and window creation:

In the Emscripten backend, the function swfw_make_context probably won't do anything, but its hints can still be used in the function swfw_make_window. One of the functions will probably be the name of the canvas HTML element that will be used.

In the case of mobile, the function swfw_make_window is responsible to create one window.

For mobile, there will be no support for non hardware accelerated window. The only option will be with hardware acceleration.

The backend for mobile must be written in C, using the proper C API (Android with NDK, and iOS with the Objective-C Runtime).